Chemical modifications of cytochalasins, especially cytochalasin D, will be continued. The purpose is to prepare intermediates which can be utilized both as site-directed alkylating reagents for receptor macromolecules, as well as to immobilize the drug to supportive matrixes. The latter will be used for affinity-chromatographic retardation of acceptor binding species. Further delineation of the functional biological receptors for cytochalasin D, located in cell membrane fractions, will be mounted. These studies will be carried out primarily with blood platelet membrane preparations, and reliance will be placed on the use of tritiated cytochalasin D, in conjunction with a variety of physical-chemical techniques. A systematic examination of the phylogenetic spectrum of activity of cytochalasins, with emphasis on responses of the lower eukaryotes, will be continued. BIBLIOGRAPHIC REFERENCES: "Action of cytochalasin D on cells of established lines. III. Zeoisis and movements at the cell surface." G. C. Godman, A.F. Miranda, A.D. Deitch and S.W. Tanenbaum, J. Cell Biol., 64, 644 (1975). "Binding and subcellular localization of tritiated cytochalasin D," J. Tannenbaum, S.W. Tannenbaum, L.W. Lo, G.C. Godman and A.F. Miranda, Exper. Cell Res., 91,47 (1975).